Metal (for example, Cu) has been used for three-dimensional packaging devices. However, a micro wiring structure made of a metal wiring material such as Cu has a problem that wiring has high resistance since conduction electrons are greatly affected by inelastic scattering at an interface due to a thin line effect.
On the other hand, a nano-carbon material (for example, graphene or carbon nanotube) differing from metal has an extremely long mean free path and a high mobility. Such a material shows a possibility of achievement of low-resistance wiring in excess of Cu when it is applied to the micro wiring structure. Therefore, in the next generation three-dimensional packing devices required to achieve a finer layered structure or wiring structure, it has been considered to use the nano-carbon material, instead of Cu, for wirings, for example, to use graphene for a horizontal wiring formed by a trench and to use carbon nanotubes for a vertical wiring formed by a via hole. In particular, a depth-wise wiring is achieved by bundling a plurality of formed carbon nanotubes.
The carbon nanotubes are a cylindrical cluster of carbon atoms, which is obtained by decomposing a carbon-containing gas with catalyst metal particles used as a catalyst and bonding carbon atoms together. The carbon nanotubes can be suitably used for the depth-wise wiring in three-dimensional packing devices since they are uni-directionally grown from the catalyst metal particles. Typically, an acetylene (C2H2) gas or an ethylene (C2H4) gas is used as the carbon-containing gas to produce the carbon nanotubes,
However, when the acetylene gas is used, while lengths of the produced carbon nanotubes are aligned, the carbon nanotubes tend to be thinner and the resistance may not be decreased as expected even when the produced carbon nanotubes are used for wiring.
On the other hand, when ethylene gas is used, while the carbon nanotubes become thicker, since the lengths of the carbon nanotubes tend not to be aligned, the carbon nanotubes may not function as the depth-wise wiring even when they are bundled.